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Title: Regarding the optimization of O1-mode ECRH and the feasibility of EBW startup on NSTX-U

Abstract

Recently published scenarios for fully non-inductive startup and operation on the National Spherical Torus eXperiment Upgrade (NSTX-U) [Menard J et al 2012 Nucl. Fusion 52 083015] show Electron Cyclotron Resonance Heating (ECRH) as an important component in preparing a target plasma for efficient High Harmonic Fast Wave and Neutral Beam heating. The modelling of the propagation and absorption of EC waves in the evolving plasma is required to define the most effective window of operation, and to optimize the launcher geometry for maximal heating and current drive during this window. Here in this paper, we extend a previous optimization of O1-mode ECRH on NSTX-U to account for the full time-dependent performance of the ECRH using simulations performed with TRANSP. We find that the evolution of the density profile has a prominent role in the optimization by defining the time window of operation, which in certain cases may be a more important metric to compare launcher performance than the average power absorption. This feature cannot be captured by analysis on static profiles, and should be accounted for when optimizing ECRH on any device that operates near the cutoff density. Additionally, the utility of the electron Bernstein wave (EBW) in driving currentmore » and generating closed flux surfaces in the early startup phase has been demonstrated on a number of devices. Using standalone GENRAY simulations, we find that efficient EBW current drive is possible on NSTX-U if the injection angle is shifted below the midplane and aimed towards the top half of the vacuum vessel. However, collisional damping of the EBW is projected to be significant, in some cases accounting for up to 97\% of the absorbed EBW power.« less

Authors:
ORCiD logo [1]; ORCiD logo [2]
  1. Princeton Univ., NJ (United States). Dept. of Astrophysical Sciences
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1432061
Grant/Contract Number:  
AC02-09CH11466
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Plasma Physics and Controlled Fusion
Additional Journal Information:
Journal Volume: 60; Journal Issue: 6; Journal ID: ISSN 0741-3335
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Electron Cyclotron; startup; spherical tokamaks

Citation Formats

Lopez, Nicolas, and Poli, Francesca M. Regarding the optimization of O1-mode ECRH and the feasibility of EBW startup on NSTX-U. United States: N. p., 2018. Web. doi:10.1088/1361-6587/aabaa8.
Lopez, Nicolas, & Poli, Francesca M. Regarding the optimization of O1-mode ECRH and the feasibility of EBW startup on NSTX-U. United States. doi:10.1088/1361-6587/aabaa8.
Lopez, Nicolas, and Poli, Francesca M. Thu . "Regarding the optimization of O1-mode ECRH and the feasibility of EBW startup on NSTX-U". United States. doi:10.1088/1361-6587/aabaa8.
@article{osti_1432061,
title = {Regarding the optimization of O1-mode ECRH and the feasibility of EBW startup on NSTX-U},
author = {Lopez, Nicolas and Poli, Francesca M.},
abstractNote = {Recently published scenarios for fully non-inductive startup and operation on the National Spherical Torus eXperiment Upgrade (NSTX-U) [Menard J et al 2012 Nucl. Fusion 52 083015] show Electron Cyclotron Resonance Heating (ECRH) as an important component in preparing a target plasma for efficient High Harmonic Fast Wave and Neutral Beam heating. The modelling of the propagation and absorption of EC waves in the evolving plasma is required to define the most effective window of operation, and to optimize the launcher geometry for maximal heating and current drive during this window. Here in this paper, we extend a previous optimization of O1-mode ECRH on NSTX-U to account for the full time-dependent performance of the ECRH using simulations performed with TRANSP. We find that the evolution of the density profile has a prominent role in the optimization by defining the time window of operation, which in certain cases may be a more important metric to compare launcher performance than the average power absorption. This feature cannot be captured by analysis on static profiles, and should be accounted for when optimizing ECRH on any device that operates near the cutoff density. Additionally, the utility of the electron Bernstein wave (EBW) in driving current and generating closed flux surfaces in the early startup phase has been demonstrated on a number of devices. Using standalone GENRAY simulations, we find that efficient EBW current drive is possible on NSTX-U if the injection angle is shifted below the midplane and aimed towards the top half of the vacuum vessel. However, collisional damping of the EBW is projected to be significant, in some cases accounting for up to 97\% of the absorbed EBW power.},
doi = {10.1088/1361-6587/aabaa8},
journal = {Plasma Physics and Controlled Fusion},
number = 6,
volume = 60,
place = {United States},
year = {Thu Mar 29 00:00:00 EDT 2018},
month = {Thu Mar 29 00:00:00 EDT 2018}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on March 29, 2019
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